1. Field of the Invention
The present invention relates to a liquid crystal display device, and particularly to a liquid crystal display device which controls a gap between two substrates thereof by using columnar spacers.
2. Description of the Related Art
A liquid crystal display device is configured by inserting a liquid crystal layer between a thin-film transistor (TFT) substrate and an opposite substrate. Columnar spacers are used for holding a gap between the TFT substrate and the opposite substrate.
On the opposite substrate, light shielding means which surrounds one or plural pixels is disposed in a grid shape. This light shielding means is called a black matrix. In the case of providing the columnar spacers on the opposite substrate, the columnar spacers are formed on portions shielded by the grid-shaped black matrix so as not to affect an aperture ratio of the liquid crystal display device. Usually, the columnar spacers are arranged on widthwise center portions of the black matrix. Above the TFT substrate, the columnar spacers are arranged on intersections of scan lines and signal lines.
After the columnar spacers are provided on the black matrix of the opposite substrate, an orientation film made of polyimide resin or the like is formed on the opposite substrate including surfaces of the columnar spacers. A treatment called rubbing is performed for a surface of the orientation film in order to impart thereto controllability for liquid crystal orientation. However, the columnar spacers are formed in a protrusion shape. For this reason, in a peripheral portion of each columnar spacer, a shaded portion where rubbing becomes insufficient sometimes occurs in a rubbing step. On such a surface of the orientation film, which has been shaded in the rubbing, the liquid crystal orientation becomes disturbed because sufficient controllability for the liquid crystal orientation cannot be imparted to the surface concerned, thus causing light leakage.
A solution technology for such a problem in the case of using the columnar spacers is disclosed in Japanese Patent Laid-Open Publication No. H11-218771 (published in 1999). In a liquid crystal display device in this publication, arranged positions of columnar spacers are set at positions which are adjacent to intersections of a square black matrix disposed in a grid shape and shifted to an upstream side of rubbing. These positions are set such that shades in the rubbing remain within a plane of the black matrix. With this arrangement structure, almost all of the shades in the rubbing are made to remain within a region of the light shielding means.
However, even with such a structure as described above, there remains a problem of “black haze” which remains after application of external force to a screen of the liquid crystal display device and removal thereof. For example, in the case where the screen of the liquid crystal display device is pushed by hand or the like and then released when black is displayed, display unevenness remains on a portion of the screen, which has been pushed by hand, without disappearing for a while. This display unevenness is caused by frictional force between the columnar spacers provided on the opposite substrate and the surface of the TFT substrate. When the frictional force is large, the display unevenness remains for a long period of time.